This Startup Says It’s Figured Out How to Trap Carbon Affordably

In the overlapping worlds of climate science and Silicon Valley, there are a great many people who say that building huge systems to remove carbon from the atmosphere is going to become a massive business—in fact, that it will have to be if humanity is to have a chance of keeping the earth’s warming to relatively safe levels. Startups in the brand new space are trying dozens of approaches, from massive fans to suck carbon dioxide out of the air, to schemes that would gather biomass from leftover crop waste, convert it into carbon-rich slurry, and then pump it underground (plants absorb carbon dioxide as they grow, and if they are left to decompose naturally, they release that carbon back into the atmosphere.)

One of the main factors holding back these methods of capturing and removing carbon emissions is cost. Most of the current technologies are currently extremely expensive—often costing around $600 for every ton of sequestered CO2. Academics and industry experts generally agree that getting costs down below $100 per ton of sequestered CO2 would be the point at which, economically, such massive carbon capture schemes become feasible. Many of the largest carbon removal startups project that level of affordability is years or even decades away.

A Bill Gates-backed startup called Graphyte, however, says it’s hit that cost benchmark. In an announcement this morning, Graphyte claims that its new carbon sequestration technique beats the $100 per ton bar—though it declined to specify exactly what its internal cost per ton is. It has not completed a pilot plant yet—that facility will come next year—but it says there’s nothing holding it back from rapidly scaling up. (The company has not yet sold the carbon removal service to potential buyers, but it says it will be announcing offtake agreements soon.)

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Graphyte’s approach, which it refers to as carbon casting, works by gathering crop waste or other carbon-rich biomass, drying it, and compressing it into large blocks. Then the blocks are sealed with a special polymer, stacked, and buried, with sensors to monitor the carbon blocks to make sure that the sealant is holding up (if the sealant is broken, the block of biomass would likely start to decompose, releasing CO2 back into the atmosphere). Graphyte says its approach will keep that carbon securely stored for 1,000 years or longer.

“Speaking as someone that’s been in this space for close to 20 years, this is the best idea out there,” says Barclay Rogers, the company’s CEO and co-founder. He says the $100 per ton price he’s shopping potential buyers is based on prices that equipment and biomass suppliers are offering him. “This isn’t Graphyte sitting around with spreadsheets dreaming what we think the cost might be,” he says.

Rogers says that the low cost is primarily due to two factors. The first is that their process doesn’t require large amounts of energy in order to work, unlike the methods of sucking carbon right out of the air, known as direct air capture. And unlike other processes that heat biomass to convert it into high-carbon products like charcoal, which are then stored, Graphyte doesn’t release a lot of the carbon they’re trying to store as exhaust in the processing. Less wasted carbon, means more carbon stored per ton of biomass they take in, and a lower cost overall.

“I don’t think it’s as scientific or as sexy as some of the other approaches,” says Chris Rivest, a partner at Breakthrough Energy Ventures, a climate-oriented venture capital firm founded by Gates, which is funding Graphyte. (Rivest is also the originator of the carbon casting idea.) “This is one of the approaches that was really purpose built to solve the long term problem of carbon capture.”

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An initial question that springs to mind upon hearing of such a method is whether the carbon will really stay where Graphyte is putting it. A lot hinges on how tough the polymer barrier around the biomass blocks turns out to be, and whether it will hold up underground for decades and centuries without allowing in moisture that would start to rot the stored biomass. The company and its backers say they have conducted extensive tests, pounding their polymer with water and UV light, for instance, to ensure it will hold up being buried for centuries. “We’re able to perform what’s called accelerated aging testing,” says Rogers. “This is effectively simulating the environmental stresses that the materials would see over 1,000 years.”

The company, however, will not reveal what its impermeable layer is actually made of. “It is a polymer barrier that has been designed to have the right durability properties [and] diffusion properties against moisture, oxygen, methane, etc.,” says Rivest.

Besides cost, the other major factor standing in the way of new carbon sequestration companies making a difference in the climate is scale. The largest carbon removal schemes have pulled on the order of a few thousand tons of carbon out of the atmosphere each. To make a real difference in the climate, however, such measures would have to be expanded to a mind-boggling scale, on the order of billions of tons.

Rogers and Rivest say there isn’t much stopping their approach from reaching that scale. Biomass, which is also useful for making the e-fuels likely necessary to decarbonize sectors like shipping and air travel, is probably going to start costing more in the decades ahead as demand heats up. The company says it is anticipating those cost increases. It says that there may have to be important decisions made about what to do with the limited biomass society does have. There’s a case to be made that it should go to Graphyte, Rivest says, since they will have a high efficiency in converting that plant matter into negative carbon.

Rogers says that the company’s first pilot plant—christened Loblolly—will be completed next year, and located in Pine Bluff, Ark. The facility will, at first, be able to process and store carbon at a rate of about 5,000 tons per year, but the goal is to expand that processing capacity to a rate of 50,000 tons per year in 2024 as well.

Another question, when talking about storing tens of thousands of tons of carbon blocks, is where Graphyte will bury all this stuff. Rogers says the company is “very close to a lock” on a site to bury their carbon, but that there’s plenty of places they can conceivably put it. Unlike many carbon storage ideas, Graphyte doesn’t need to find places with the right geology to inject carbon deep underground. Asked about the feasibility of trucking all those blocks around and digging holes to put them in, Rivest says that’s something modern society does plenty of already.

“The world doesn’t take its refuse and turn it into oil and inject it underground, right?” Rogers says. “They put it in landfills, and so that just at its core suggests that the most cost effective way of dealing with material of this nature is through shallow underground storage.”

Later on, he clarifies: Graphyte is not proposing to landfill the world’s carbon emissions. “It’s constructed in a more engineered way than that,” Rogers says of the planned storage locations. “It has these high tech sensors in it. It doesn’t have decomposing waste. There’s many, many things that are different to these storage sites than a landfill.”